1. Field of the Invention
The present invention relates to a radio system realizing a wireless subscriber interface, the system including a subscriber station which comprises means for forwarding, on the radio path, a supervisory signal received on the radio path, a base station which comprises supervisory means for producing and transmitting said supervisory signal on the radio path to the subscriber station and for monitoring the connection between the subscriber station and the base station on the basis of the supervisory signal returned by the subscriber station, and a subscriber network element which comprises means for forwarding, on the radio path, communication signals between a communication system and the subscriber station via the base station, and a control unit for controlling the supervisory means of the base station. The invention further relates to subscriber station in a radio system realizing a wireless subscriber interface, the subscriber station having a radio section and a user interface, whereby the radio section comprises means for establishing, by means of radio frequency signals, a communication link between the user interface and a communication system, the subscriber station having means for forwarding, on the radio path, a predetermined supervisory signal received on the radio path.
The present invention particularly relates to forwarding, by means of radio signals, charging information to a chargeable subscriber station, such as a coin box telephone, which communicates with the communication network. The invention particularly relates to a Wireless Local Loop (WLL) system, i.e. a radio system constituting a wireless local loop wherein subscriber stations are connected to the public switched telephone network (PSTN) by a radio connection. Any conventional telephone set can be connected to the WLL system with a specific terminal equipment, resulting in that the radio path is transparent as far as the user is concerned.
2. Description of the Related Art
The term subscriber station here refers to the equipment which the subscriber has at his disposal for transmitting and receiving communication signals, i.e. in case of a WLL system, the subscriber station includes a WLL terminal consisting of a radio section and a tele adapter (to which the user interface, such as a telephone, is connected), as well as a user interface such as a telephone, telefax, computer/modem combination or the like to be connected to the terminal equipment. The term chargeable subscriber station here refers to a type of a subscriber station that charges the user immediately in connection with the use, and most often at least partly in advance. The chargeable subscriber stations denote subscriber stations that comprise user interfaces operating with coins, credit cards or similar methods of payment, i.e. interfaces such as coin box telephones or telefax terminals.
In connection with the use of chargeable subscriber stations, the system must be able to charge the user of the subscriber station during the use. The fixed telephone network commonly employs 12 kHz or 16 kHz home metering pulses to transmit charging information. As the width of the speech band in radio systems is, for practical reasons, significantly narrower than the width of the speech band in the fixed telephone network, the aforementioned frequencies do not usually fall within the speech band of radio systems. Therefore, the home metering pulses have to be sent to the subscriber stations of the radio system on some other frequency.
A prior art solution is utilized in association with chargeable subscriber stations in, for example, the NMT system, wherein a tariff frame is transmitted on the radio path to a coin box telephone in connection with call set-up. On the basis of the tariff frame, the phone charges its user independently for the duration of the entire call. A drawback of this prior art solution is that it cannot take into account tariff changes possibly taking place during the call. It is common practice that the operator defines a separate evening tariff, which may differ considerably from the day-time tariff. However, the aforementioned prior art solution is not able to take into account that the tariff may change during a call with the result that the user of a coin box telephone ends up paying significantly more (or less) for the call than the operator considers the true charge of the call to be. In other words, the charge determined by the exchange for the call may differ considerably from the sum charged by the coin box telephone from the user. The above also presents a disadvantage for conventional phones if a pulse counter has been connected to the phone. The reading on the counter may in such a case differ from the reading determined by the exchange and used for charging the subscriber.